1. Field of the Invention
The present invention relates to a magnetic element containing a coil wound around a magnetic core. In particular, the present invention relates to an inductor component, for example, a transformer and inductor, used for a step-up and step-down choke coil, transformer, power transformer, etc., for an inverter switching power supply and applied with a direct-current bias.
2. Description of the Related Art
Hitherto, the aforementioned type of inductor component has been configured as follows. First, a coil has been wound around a columnar material in a drum magnetic core. The magnetic core has been made of a magnetic material and has had a structure including integrated disk flanges at both ends of the columnar material. A cylindrical insulating material has been placed on the periphery thereof. A cylindrical sleeve core has been further placed on the periphery of the insulating material. A terminal has been placed at a predetermined position in the neighborhood of the bottom portion of the cylindrical sleeve core in order to connect with a lead wire of the coil end portion.
Regarding the inductor component based on the conventional technique, the cylindrical sleeve core is fitted to the outside of the drum magnetic core and, thereafter, the cylindrical insulating material is inserted into the joint portion of the drum magnetic core and the cylindrical sleeve core. Consequently, a gap is included in the configuration, a magnetic field Hs is generated by a magnetomotive force; due to the coil, and the magnetic field H5 acts from one flange toward the other flange side.
Accompanying recent miniaturization and weight reduction of electronic apparatuses, demand for miniaturization has occurred with respect to inductors and transformers used for power supply portions. When a whole structure is miniaturized, a drum magnetic core becomes likely to magnetically saturate and, therefore, a problem occurs in that a treatable current is reduced. Regarding the aforementioned configuration of the inductor component, this problem can be overcome by enlarging the gap due to the insulating material. However, the number of turns of the coil must be increased because a value of inductance is reduced and, therefore, realization of miniaturization is hindered.
Some inductor components have overcome such a problem. In the configuration of an example of the aforementioned inductor components, a coil is wound around a columnar material between flanges at both ends of the drum magnetic core made of a magnetic material and having a structure including integrated disk flanges at both ends of the columnar material, a cylindrical permanent magnet is placed on the periphery thereof, and a terminal is formed on a predetermined position in the neighborhood of the bottom portion of the permanent magnet in order to connect with a lead wire of the coil end portion.
That is, regarding this inductor component, a cylindrical permanent magnet is placed instead of the sleeve core on the outside of the drum magnetic core while the south pole side is arranged at one flange side and the north pole side is arranged at the other flange side. According to such a configuration, the magnetic field Hs is generated by a magnetomotive force due to the coil, and acts from one flange toward the other flange. A magnetic field HM due to the permanent magnet acts to obstruct this magnetic field Hs. Consequently, the treatable current can be increased by application of a magnetic bias.
Regarding this inductor component of magnetic bias application-type, the drum magnetic core is manufactured by using a Nixe2x80x94Zn-type ferrite powder, compact molding by a press method, thereafter sintering or pressing the ferrite powder into the shape of a cylinder column, sintering, and, thereafter machining so as to manufacture the flange portions and, therefore, the drum magnetic core is manufactured. The permanent magnet for applying a magnetic bias is manufactured by the steps of performing compact molding of a powder of Sr ferrite, Ba ferrite, etc., by a press method and, thereafter, performing sintering, and is integrally joined using an adhesive, etc., at the time of fitting to the drum magnetic core with a coil wound around.
The following disadvantages are listed with respect to the inductor component of magnetic bias application-type based on the conventional technique.
The first problem is in that since an open magnetic circuit is configured without the use of sleeve core in the adopted structure, leakage flux is likely to increase and affect the surroundings and, therefore, measures for magnetic shielding cannot be taken adequately.
The second problem is in that the open magnetic circuit is configured without the use of sleeve core in the adopted structure, the effective permeability is reduced, the inductance is reduced, and, therefore, the coil must have a large number of turns (the coil is long-wound) in order to achieve a required inductance value resulting in hindrance of miniaturization The third problem is in that when a ferrite powder is used for the permanent magnet, thermal demagnetization is likely to occur accompanying heating during the step of reflow soldering and demagnetization is likely to occur due to an excessive current and, therefore, the magnetic characteristics of the permanent magnet are likely to be degraded.
The fourth problem is in that when a metal-based material is used for the permanent magnet, an eddy current loss is increased due to the low resistivity, permanent demagnetization occurs due to proceeding of oxidation with time and, therefore, initial characteristics cannot be maintained as the magnetic characteristics. This problem is fatal to the reliability.
Accordingly, it is an object of the present invention to provide an inductor component capable of treating a large current, having magnetic characteristics unlikely to be degraded, and suitable for taking measures for magnetic shielding, miniaturization, and weight reduction with ease.
It is another object of the present invention to provide an inductor component capable of reducing the processing cost based on shortening of the process by performing the step of magnetization of the permanent magnet and the step of adhesion and fixing of the permanent magnet to the magnetic core in a single step.
It is still another object of the present invention to provide a manufacturing method for the aforementioned inductor component.
According to an aspect of the present invention, there is provided an inductor component which contains a drum magnetic core made of a magnetic material having a structure including integrated flanges at both ends of a columnar material, a coil wound around the columnar material in the drum magnetic core and placed between the flanges, and a permanent magnet placed in the neighborhood of the drum magnetic core with the coil wound around. A sleeve core is fitted to the outside of the drum magnetic core. The permanent magnet is placed in at least one gap in a closed magnetic circuit formed with the drum magnetic core and the sleeve core in order to apply a direct-current magnetic field in the direction opposite to the direction of a magnetic field generated by a magnetomotive force due to the coil.
According to another aspect of the present invention, there is provided a manufacturing method for an inductor component is provided. The inductor component contains a drum magnetic core made of a magnetic material having a structure including integrated flanges at both ends of a columnar material, a coil wound around the columnar material in the drum magnetic core and placed between the flanges, and a permanent magnet placed in the neighborhood of the drum magnetic core with the coil wound around. The manufacturing method includes the steps of fitting a sleeve core to the outside of the drum magnetic core, and placing the permanent magnet in at least one gap in a closed magnetic circuit formed with the drum magnetic core and the sleeve core in order to apply a direct-current magnetic field in the direction opposite to the direction of a magnetic field generated by a magnetomotive force due to the coil.